Washing



Feb. 21, D CLARK WOOD PULPING PROCESS 2 Sheets-Sheet 1 Filed Sept. 24,1955 Mm G O G m m m N NE W Iv M -v u u V E GH A U S F R T A A P D S W WW W G N N G 6 PE m w m m mm W K v H YPR E D 0 S O F m w M my A A W C S GW G PE m A m mm M H i mw W NM 5 OT F M A TS A H w w m TO PU LP STORAGEINVENTOR.

ATTORNEYS.

Feb. 21, 1956 D A: ARK

WOOD PULPING PROCESS 2 Sheets-Sheet 2 1 Filed Sept. 24, 1953 IN VEN TOR.

ATTORNEYS.

United States Patent WOOD PULPING PROCESS James dA. Clark, Longview,Wash. Application September 24, 1953, Serial No. 382,065

Claims. (Cl. 92-6) This invention relates to the conversion of woodymaterial to release pulp fibers for use in the manufacture of papers,boards and other felted fibrous structures, and it relates moreparticularly to a pulping process which releases fibers from woodymaterial in a more eificient and economical manner without deteriorationof the fibers or loss in the strength properties thereof to enable usein the manufacture of lower cost and higher strength fibrous structures.

To the present, various means have been used to reduce woody material toparticle sizes suitable for digestion by chemical reactions for theelimination of ligneous binders and release of the fibers as pulp forthe preparation of fibrous structures. Little attention has been givento the manner in which the woody material has been disintegrated forreduction to particle sizes suitable for digestion with cooking liquors.

It has been found in recent investigations that in the use ofconventional devices for disintegration, the wood is crushed or bruisedparticularly in zones beneath the new surfaces formed upon division andthat the degree of crushing is out of proportion with the extent ofreduction in particle size.

Recent investigations have also established quite conclusively that thecooking liquors used in the digestion processes tend to attack thecellulosic materials in the bruised areas more violently than theremainder with the result that wooden elements containing bruisedportions have been found to produce inferior pulp and the fibrousstructures fabricated therefrom have been found to embody less strengthas compared to the use of particles containing lesser proportions ofbruises. Green and Yorston (Pulp and Paper Magazine of Canada, 41, No.2: 123-126 February 1940) have found that fibrous chips which have beenpartially crushed in the manner described during preparation and priorto cooking produce pulp having about one-half the tensile or burststrength, about one-third the tearing strength and about onetwentieththe folding endurance as compared to pulp formed of wooden chips whichhave been prepared without cmshing. Crushing which causes degradation ofthe type described in wood fibers has been found to result also if thinslices of wood for digestion are planed or sliced from a block of woodwith the cutting edge placed at right angles to the grain and movedalong the grain. Degradation in such fibrous elements occurs mostlyadjacent the side of the slice away from the block and is believed toresult from the crushing of the slice by compression of the woodymaterial on the side toward which the slice curls. Although thecompression is gentle, such unbelievable losses in strength result thatlittle doubt remains as to the degradation of the fibers which takesplace in this form of planing process.

These results have been confirmed in actual practice but the reason forthe deterioration of pulp from such material has been attributed toother factors. When the size of the chips is reduced, such as to belowinch, the

quality of the resulting pulp has been found to commence theories forthe deterioration in the characteristics of pulp made from fine woodparticles; most of the theories have centered upon the concept thatharmful results are secured because of excessive cutting of the fibersin the wood and the adverse effect of the fine material upon liquorcirculation. Now it appears that the principal factor resides in thediscovery of the adverse effect of bruising and crushing which increasesin proportion inversely with the size of the wooden particle.

Because of the misleading hypotheses with respect to chipping which havein the past been accepted by those skilled in the art, there has been noincentive to search for means for greater size reduction notwithstandingthe apparent economies and efliciencies in operation based upon the morerapid penetration of the cooking liquor into the smaller particles witha yield of a more uniform pulp.

Another reason for the persistent adherence to present practice inchipping and cooking woody materials in the manufacture of pulp has beenthe unavailability of devices of sufiicient capacity for effecting sizereduction without excessive damage to the fibers in a practical and yeteconomical manner.

It is an object of this invention to provide a new and improved methodfor reducing woody material in the manufacture of pulp and it is arelated object to provide a continuous process for achieving same whilepreserving the inherent strengths of the pulp fibers.

Another object is to provide a new and improved process whereby woodymaterial is reduced for use in the manufacture of pulp with a minimumamount of crushing and bruising of the fibers and in a form whichpermits rapid and economical reaction with the cooking liquors toproduce a pulp of high yield and of high strength for use in themanufacture of improved fibrous structures.

Other objects and advantages of this invention will hereinafter appearand for purposes of illustration, but not of limitation, embodiments ofthe invention are shown in the accompanying drawing in which:

Figure 1 is a diagrammatic perspective elevational view illustrating theconcepts in the reduction of woody materials into wafers for use in themanufacture of pulp in accordance with the practice of this invention;

Figure 2 is a photomicrograph of the surface of a wafer produced inaccordance with the illustrated process of Figure 1;

Figures 3, 4 and 5 represent flow sheets for the preparation of pulpwith fibrous elements of the type described.

It has been found, in accordance with the practice of this invention,that when the woody material, such as a wooden block 10, is cut intowafers 11 with a cutting edge 12 held parallel to the grain of the woodbut adapted to cut across the grain, as distinguished from along thegrain, the wafer, as it is being severed, will curl as previouslydescribed but curling will occur lengthwise along the axis substantiallyparallel to the grain of the wood so that little, if any, stresses areimposed on the cellulosic fibers which might result in the damage orcrushing thereof. As a result, the fibers remain in condition to resistexcessive attack by the cooking liquors and they retain their originalcharacteristics for use in the manufacture of an improved pulp and themanufacture of fibrous structures of greater strength and uniformity atlower cost.

As. will be apparent from the photomicrograph of the wafers 11 severedin the manner described from the wooden block 10, very little damage hasbeen found to occur to the fibers on the cut surface of the wafer. Thevast differences in pulp formed as between the use of crushed chips anduncrushed chips of wood and as between chips and wafers prepared inaccordance with the practice of this invention can be illustrated by theresults listed in the following table which compares the pulps formed'ofcrushed and uncrushed chips of Idaho spruce and the pulps of uncrushedchips and wafers of Eastern spruce, all of which have been uniformlyprocessed in accordance with the flow sheet outlined in Figure 3. Theresults process for preparing pulp in accordance with the practice ofthis invention. Figure 4 shows another schematic process for preparingpulp whereby the cooking chemical Evaluation of beaten pulp from wafersand from chips Percent Yield Screen classification Bulk Burst TearTensile Folds Sample v 1 i ec./g. metric metrlcm. N0. Retained 28/200,Passed Total Rejects 28 mesh mesh 200 mesh Uncrushed Chips, I. S 1. 27121 103- 88. 9 7. 9 3. 2 0.04" thick wafers, I. S 1. 25 125 126 87. 4 9.3 3.1 0.01" thick \i 'afers, I. S 1.21 115 99 77. 7 16. 4 5. 9 UpcrushedChips, E. S 1.18 116 83 71. 8 17. 8 10. 4 Crushed Chips, E. S- 1.17' 4250 17. 71.1 11.4

E. S.=Eastern spruce. I. S;= Idaho spruce;

It will be apparent from the results that a three-fold increase inburst. strength and better than a 60 percent increase in tear andtensile strength is achieved with the use of uncrushed chips as comparedto crushed chips of the types which have heretofore been prepared foruse in the pulp and paper industry. Also a -fold increase in the numberof folds is secured with pulp formed of uncrushed chips of Easternspruce. Theseresults fully confirm the work previously noted, of theCanadian Forest Products Laboratory.

With the establishment of the fact that deterioration of the pulpresults primarily from the presence of crushed fibers rather than beingdependent entirely'on the particle size of the wooden material fed intothe cooking liquor, it became desirable to achieve means whereby suchuncrushed wooden elements could be produced in anefficient and.practical manner and preferably in aform adapted for use in thepreparation of pulp by the usual cooking processes substantiallycompletely to reduce the wooden elements to pulp without excessiveattack and withoutuncooked portions which otherwise woud have to bediscarded as waste.

As previously described, wooden wafers substantially free of bruises anddamage by crushing can be produced by cutting the wood with a cuttingedge held parallel to and advanced across the grain to sever the wafersfrom the wooden block. In the manufacture of such wafers, it ispreferred to score the wood transversely to the grain to'define thelength of the wafers in situ and then to sever the wafer as an entityfrom the scored surface ofv the wood with cutting edges heldsubstantially parallel to the grain and to cut across the grain.Alternatively, the wafers may be economically produced in an efircientmanner by means of alternate scalloped and straight edged kniveshavingtheir main cutting edges held parallel to the grain and adapted to passacross the grain of the wood. Suit-- ablewaferizers for use inthereduction of wooden blocks. into elements for pulping are describedin my copending applications Ser. No. 375,152, Ser. No. 344,089, andSer. No.- 383,893. The apparatus described in the latter application iscapable of the very large capacity desired for pulp manufacture, suchfor example as better than 200 tons of wood per day.

It will also be apparent from the previous table that the pulp securedfrom wafers prepared in the manner described is superior to pulpprepared of chips which have been carefully formed to prevent crushing.Advantages have been found not only to result in the improved propertiesof the pulp and the fibrous structures formed there of but thecontrolled and uniform dimension of the wafers enables more rapid andmore uniform digestion with the cooking liquors to the end that theyield is greatly int-- proved and rejects in the form ofchips whichhave.not been cooked are substantially completely avoided.

Various processes well known to the trade may be used. to convert thewafers: into pulp for use in the manufacture of fibrous structures.Figure 3 showsa schematic is added to the wafers and the wafers andchemical are thereafter introduced together into a cooking chamberthrough apressure seal. The material progresses along and through thecooking chamber and immerges through another seal to be washed forremoval of the cooking. chemicals, as in conventional practice.

Figure 5 illustrates a modification of the process outlined in Figure.4. In this process, the wafers are first impregnated with the cookingliquor whereby absorption occurs very uniformly and rapidly, especiallyif. the liquor is hot. The excess liquor isdrained from the wafers andthey are thereafter subjected to heat and pressure in a closed chamberfor a period of time sufiicient to permit the residual liquor to cookthe woody material to the desired degree. The waters are thereafterremoved from the cooking vessel and washed.

Various modifications may be made inaddition to those described withoutdeparting from the spirit of the invention. For'instance, in the systemsillustrated in Figures 4, 5 or 6, the cooking may be accomplished withina steam chamber equipped with a rubbing or disintegrating means, such asa' pair of discs, paddles or screws, well known: in the art.

Because of the gradual depletion of our forests, it has become desirableto make use of pulping processes which provide for higher yield. Onesuch process which is readily available for use with wafers prepared inaccordance with this invention comprises a semi-chemical process whereinthe woody chips are given a relatively mild cook in which the percentageof active chemical, the time or temperature is restricted so that theiryield of pulp will be in excess of 60 percent. The partially softenedchips are then disintegrated by various suitable refining means wellknown in the art. It will be evident that a Wafer produced in the mannerdescribed, when softened by cooking and then rubbed, will have a decidedpreference for separating along the grain into long slenderfiber'bundles and ultimate fibers, and it may be soreduced by a verygentle mechanical action, requiringv little power and doing very littledamage to the fibrous elernents. A semi-cooked chip of the type hithertoused has, after cooking, a hard resistant interior which must be mashedand cut in present semi-chemical processes in order. to reduce. it, withthe result that by the time the chip has been disintegrated, the productconsists: of excessively short fibers and debris capable of use only informing a relatively weak and inferior product.

As a result, the use of Wafers instead of chips of the type heretoforeproduced for the manufacture of pulp by a semi-chemical process providesmarked advantages, even in those processes which rely upon the woodparticles being defibered as they are softened under steam prcssure in.such equipment as the Asplunddefibrator, esp,e-' cially if used. inconjunction with a continuous pro-cooker, as: is now common practice.

It will be'apparent further from the table previously set forth that thepulping process depends in part upon the thickness of the wafers cut.The preferred thickness of wafers is in the order of about 0.03 to 0.07inch but the thickness may be varied without interfering with theprocess other than to lengthen the time necessary for suitablepenetration of the cooking liquor sidewise into the fibers as thethickness of the wafer is increased. However, it is undesirable to makeuse of wafers having a thickness less than 0.01 inch or greater than 0.1inch. A convenient length of the wafer for purposes of digestion isabout 2.5 inches. Since the liquor penetrates along the grain aboutfifty to one hundred times faster than it does across the grain, a ratioof length to thickness of about 50 or more is desirable. When very sharpknives are used, the wafers can be cut thinner if desired to speed upthe absorption of the cooking liquor and the lengths of the wafers mayvary in amounts convenient for handling but it is undesirable to makeuse of wafers having lengths greater than 5 inches.

It will be evident from the foregoing that there is provided a processfor the reduction of woody material into elements capable of use in theproduction of high quality pulp wherein the strengths of the fibersremain substantially intact as a result of the reduction of the woodymaterial without deterioration of the fibers in the reduction process asby crushing or bruising. It will be evident further that the process ofthe type described for the reduction of woody material produces wafersof a controlled dimension for most eflicient penetration of the cookingliquors to enable uniform and complete reduction to pulp thereby toeliminate waste and to minimize attack on the pulp fibers during thecooking process.

It will be understood that changes may be made in the details ofproduction of the wooden wafers within the limitations described and theprocessing thereof into pulp without departing from the spirit of theinvention, especially as defined in the following claims.

I claim:

1. In the method of pulping wood, the steps of reducing blocks of woodinto wafers of substantially uniform dimension by cutting the face ofthe wooden block with cutting edges parallel to and moved across thegrain into Wafers having a width corresponding to the width of theindividual cutting edges, a thickness ranging from 0.01 to 0.1 inch anda length up to 5 inches, said wafers being produced without crushing orbruising, treating the wafers with cooking liquor, and then reducing thecooked wafers into pulp.

2. In the method of pulping wood, the steps of cutting the wood in oneface of a block with cutting edges parallel to and moved across thegrain into wafers having a thickness of 0.01 to 0.1 inch and ofrelatively uniform length and width whereby the fibers in the wafers 6the wood into wafers of substantially uniform dimension by cutting ablock of wood with cutting edges parallel to and moved across the graininto wafers of uniform dimension whereby the fibers in the Wafers remainrelatively free of deterioration by crushing and bruising, treating thewafers with a cooking liquor, and then reducing the cooked wafers intopulp.

6. In the method of pulping wood, the steps of reducing blocks of woodinto wafers of substantially uniform dimension by cutting the face ofthe Wooden block with cutting edges parallel to and moved across thegrain into wafers having a width corresponding to the width of theindividual cutting edges, a thickness ranging from 0.01 to 0.1 inch anda length about fifty times the thickness but less than 5 inches, mildlycooking the wafers in a semi-chemical process in which the activechemicals and the time and temperatures are controlled partially tosoften the bonding agent holding the fibers together in the wafer, andsubjecting the partially cooked wafers to gentle mechanical action forseparation of the fibers along their grain without damage to the fibrouselements to form pulp fibers.

7. In the method of pulping wood, the steps of reducing blocks of woodinto waters of substantially uniform dimension by cutting the face ofthe wooden block with cutting edges parallel to and moved across thegrain into wafers having a width corresponding to the width of theindividual cutting edges, a thickness ranging from 0.01 to 0.1 inch anda length up to 5 inches, treating the wafers under controlled conditionsof time, temperature and with chemicals partially to cook the wafers,and rubbing the partially cooked wafers to separate the fibers along thegrain without damage to the fibrous elements to form the pulp fibers.

8. In the method of pulping wood, the steps of reducing the wood bychemical and mechanical treatment to form pulp by'cutting the wood witha cutting edge parallel to and moved across the grain into wafers ofsubstantially uniform thickness whereby the fibers extend longitudinallyin the wafer and remain relatively free of deterioration by crushing andbruising, mildly cooking the wafers in a semi-chemical process in whichthe active chemicals and the time and temperature are controlledpartially to soften the bonding agent securing the fibers one to anotherin the wafer, and subjecting the partially cooked wafers to a gentlemechanical action to efiect separation of fibers along their grainwithout damage to the fibrous elements to form pulp fibers.

remain relatively free of deterioration by crushing and bruising, thencooking the wafers, and reducing the cooked wafers to a pulp.

3. In the method of pulping wood, the steps of reducing the wood forchemical cooking to form pulp by cutting the wood across one face withcutting edges parallel to and moved across the grain into wafers havinga thickness ranging from 0.01 to 0.07 inch whereby the fibers in thewafers remain relatively free of deterioration by crushing and bruising,treating the wafers with an acid cooking liquor and then reducing thecooked wafers into pulp.

4. In the method of pulping wood, the steps of reducing blocks of woodfor chemical cooking to form pulp by cutting the blocks in one face withcutting edges parallel to and moved across the grain into wafers havinga thickness within the range of 0.01 to 0.1 inches and a length greaterthan about fifty times the thickness but less than five inches wherebythe fibers in the wafers remain relatively free of deterioration bycrushing and bruising, treating the wafers with a cooking liquor, andthen reducing the cooked wafers into pulp.

5. The method of pulping wood comprising reducing 9. In the method ofpulping Wood, the steps of cutting the wood in one face of a block withcutting edges parallel to and moved across the grain to form wafershaving a relatively uniform length ranging from 0.5 to 5.0 inches and. arelatively uniform thickness ranging from 0.01 to 0.1 inch whereby thefibers in the cut wafers remain relatively free of deterioration bycutting and bruising, treating woody material comprising such waferswith a chemical solution under controlled conditions of concentration,time and temperature to soften the woody wafers, and then reducing thetreated wafers to pulp.

10. The method as claimed in claim 9 wherein the chemical treatment ofthe wafers and their reduction to pulp is performed as a continuousoperation.

References Cited in the file of this patent UNITED STATES PATENTS1,982,130 Wollenberg Nov. 27, 1934 2,323,194 Beveridge June 29, 19432,509,642 Horsak May 30, 1950 2,655,189 Clark Oct. 13, 1953 2,689,092Clark et al. Sept. 14, 1954 OTHER REFERENCES The Effect of Chipping onthe Suitability of Wood for Sulphite Pulping by Green from Pulp & PaperMagazine of Canada, pages 123-126, Feb. 1940.

1. IN THE METHOD OF PULPING WOOD, THE STEPS OF REDUCING BLOCKS OF WOODINTO WAFERS OF SUBSTANTIALLY UNIFORM DIMENSION BY CUTTING THE FACE OFTHE WOODEN BLOCK WITH CUTTING EDGES PARALLEL TO AND MOVED ACROSS THEGRAIN INTO WAFERS HAVING A WIDTH CORRESPONDING TO THE WIDTH OF THEINDIVIDUAL CUTTING EDGES, A THICKNESS RANGING FROM 0.01 TO 0.1 INCH ANDA LENGTH UP TO 5 INCHES, SAID WAFERS BEING PRODUCED WITHOUT CRUSHING ORBRUISING, TREATING THE WAFERS WITH COOKING LIQUOR, AND THEN REDUCING THECOOKED WAFERS INTO PULP.